A wireless communication environment always changes under the influence of a communication distance with a communication partner, external noise, the presence of an obstacle, or the like. To cope with such change in communication environment, a wireless communication apparatus performs transmission power control. Transmission power control is control of increasing (decreasing) transmission power in accordance with a communication error rate or information from a partner device, and minimizing the transmission output to continue communication, thereby setting an optimal transmission output.
When transmission power is larger than needed, not only power consumption increases, but also a neighboring wireless network is interfered with. Alternatively, when transmission power is too small, an error increases in a signal to be transmitted to a communication partner, resulting in communication failure in the worst case.
In an IEEE802.11 infrastructure mode, all wireless communication apparatuses communicate via a base station (access point). Hence, the base station can concentratedly control and manage the transmission power of the wireless communication apparatuses. Each wireless communication apparatus can perform transmission power control with the base station based on one-to-one communication.
Japanese Patent Laid-Open No. 11-155172 discloses a technique for decreasing the amount of interference between a wireless communication apparatus and a neighboring base station.
In an adhoc network in which wireless communication apparatuses directly communicate with each other without the intermediacy of any specific base station, in order to save power consumption, transmission power control can also be performed depending on the communication distance and communication interference level. However, since the base station is not present in the adhoc network, transmission power control of a plurality of wireless communication apparatuses cannot be concentratedly managed. Therefore, transmission power control based on one-to-one communication in the infrastructure network may pose a problem when a new wireless communication apparatus is to join a network, or when a wireless communication apparatus is to directly transmit information to a plurality of partners.
For example, when a new wireless communication apparatus is to join an IEEE802.11 adhoc network, other wireless communication apparatuses do not know the wave receiving state and communication distance between them. Assume that such new wireless communication apparatus broadcasts Probe Request in order to search for any available network. Upon reception of Probe Request, each wireless communication apparatus is to send back Probe Response. However, when the wireless communication apparatus transmits Probe Response with the same transmission power as that for a current communication partner, Probe Response may not reach the new wireless communication apparatus. In this case, the new wireless communication apparatus determines that no network is present around it, and cannot join the network.
Assume that the new wireless communication apparatus transmits an IP address confirmation request such as ARP Request in order to confirm an IP address. Upon reception of ARP Request, the wireless communication apparatus is to send back an IP address notification such as ARP Reply. However, when the wireless communication apparatus communicates with the same transmission power as that for the current communication partner, ARP Reply may not reach the new wireless communication apparatus. In this case, the new wireless communication apparatus may set an IP address identical to an IP address already in use. As a result, the communication cannot be normally performed, and data inconsistency occurs.
In the adhoc network, in addition to ARP Request, a network notification signal (BEACON signal) or the like may be required to be transmitted as a packet to the entire network or a plurality of terminals. In this case, when the packet is transmitted with the same transmission power as that for the current communication partner, the packet may not reach the entire network, and information may not be transmitted.